In this study, the P. tabuliformis plantation community in the Zhongtiao Mountain was used as the research object, contribution of understory subassemblages of different samples to the distribution pattern of community species richness has been studied, and the key species that affect the distribution pattern of species richness in the regions community have been identified. This study will provide a theoretical basis for the conservation of regional species diversity. The results show that: (1) the distribution pattern of understory species frequency in this area is obviously to the right, and there are obvious differences in species richness in different samples. (2) The contribution of common species to the distribution pattern of community richness is greater than that of rare species. (3) The most common species explained 88.4% of the species richness pattern of the entire community (P<0.01), while the rarest species only explained 24.5% (P>0.05). After removing the rarest species, the most common species can explain 90.8% of the remaining species (P<0.01), while after removing the most common species, the rarest species can only explain 48.6% (P<0.01). (4) When there are more common species in the subassemblage, the higher the correlation between the subassemblage and the richness distribution pattern of the full assemblage. (5) Forsythia suspensa, Philadelphus pekinensis, Smilax stans, Adenophora wawreana and Lonicera chrysantha contribute the most to the distribution pattern of community species richness, and not the more common species contribute more to the community richness pattern. (6) Species with low interspecific associations with more frequent species contribute more to the distribution pattern of community species, but this explanation does not apply in respect of rare species. In the process of protecting the species diversity of P. tabuliformis plantations, we should not only focus on common species and ignore rare species.